A DRAM cell is essentially a capacitor for storing charge and a pass transistor (also called a pass gate or access transistor) for transferring charge to and from the capacitor. Data stored in the cell is determined by the absence or presence of charge on the storage capacitor. Because cell size affects chip density, and cost, reducing cell area is one of the DRAM designer's primary goals.
One way to accomplish this density goal without sacrificing storage capacitance is to use trench capacitors in the cells. Trench capacitors can be formed by etching deep trenches in a silicon wafer and forming vertically oriented capacitors within each deep trench. Thus, the surface area required for the storage capacitor is dramatically reduced without sacrificing capacitance, and correspondingly, storable charge.
Trench-type memory devices are advantageous, in comparison to planar memory configurations, for increased density, performance and lithographic considerations. Trench-type memory devices increase density by reducing the cell area of each memory device, therefore allowing for closer positioning of adjacent memory devices.
As the trend towards miniaturization increases, as does the performance demands of electronic devices, it is desirable to have and improved DRAM and method of fabrication.